NADPH-cytochrome P450 oxidoreductase (CYPOR, encoded by the POR gene) deficiency has been correlated with the skeletal and steroidogenic anomalies of Antley-Bixler syndrome (ABS), although its specific effects on cytochrome P450 (CYP)-mediated xenobiotic and endobiotic metabolism remain unresolved. Forty naturally occurring human CYPOR variants, recently discovered and representing a broad range of residual activities, have been categorized based on phenotypic correlation and preliminary enzymology. This research plan is designed to address, on a molecular and cellular level, how naturally occurring POR mutations and polymorphic variations affect the structural arrangement and catalytic function of CYPOR in supporting cellular processes. Specific Aim 1 - Molecular Analysis of POR Variants will examine the hypothesis that specific residues, when mutated, produce proteins with altered electron transport and/or oxidation/reduction partner interaction properties. To address this aim, both solution (spectroscopic, kinetic, and thermodynamic) and crystallographic (X-ray diffractions) techniques will be utilized. Preliminary evidence suggests that specific deficiencies may be addressable from a therapeutic perspective. Furthermore, CYPOR deficiency, as well as the subsequent imbalance of CYP metabolites, is predicted to result in altered gene expression profiles that lead to developmental defects. Therefore, Specific Aim 2 - Cellular Analysis of Downstream Events in CYPOR Deficiency will utilize cellular models of tissues affected by varying degrees of CYPOR deficiency. To address this aim, defective POR genes will be introduced into both primary (isolated from PORlox/lox mouse tissues) and transformed human (liver, intestinal, and bone) cell models in order to measure the direct metabolic (CYP-mediated activity assays) and downstream response (functional assays and gene expression profiling) to xenobiotic/endobiotic challenge. Public Health Relevance: The relevance of this proposed work to public health is that it will investigate the multiple genetic mutations in CYPOR being found in the human population, which could influence the response to environmental and therapeutic agents during prenatal development, as well as in young and adult human beings.